Semiconductor device and fabrication method thereof

ABSTRACT

Fabrication method of a semiconductor device is provided. The method includes forming an etch layer on the substrate, forming a first transitional layer and a first barrier layer on the etch layer, forming first islands on the first transitional layer by patterning the first barrier layer, forming first trenches in the first transitional layer to expose the etch layer, transferring the pattern of the first trenches into the etch layer and removing the first island, forming a second transitional layer and a second barrier layer on the etch layer and the first trenches, forming second islands on the second transitional layer by patterning the second barrier layer, forming second trenches in the second transitional layer to expose the etch layer, and transferring the pattern of the second trenches into the etch layer.

CROSS-REFERENCES TO RELATED APPLICATION

This application claims the priority of Chinese Patent Application No.201910223038.8, filed on Mar. 22, 2019, the content of which isincorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to the field of semiconductortechnology and, more particularly, to a semiconductor device and amethod of forming the semiconductor device.

BACKGROUND

Nanolithography is currently the most powerful and mature technology inintegrated circuit fabrication. However, nanolithography has lowprecision, especially with the development of integrated circuitmanufacturing technology, nanolithography is difficult to meet theincreasing demands for high precision.

Extreme Ultraviolet Lithography is often referred to as EUV lithography.EUV lithography uses extreme ultraviolet light with a wavelength of10-14 nm as the light source, which can reduce the exposure wavelengthto 13.5 nm, thus extend the lithography to feature sizes below 32 nm.For example, the feature size can be 14 nm, 7 nm, or even 5 nm. Extremeultraviolet lights are generated by exciting the K pole of ultraviolettubes through electricity circulation. It has been proven that EUVlithography can offer high precision.

However, extensive research and development are still needed for EUVlithography to achieve a mature level that is suitable for massproduction. The use of EUV lithography machines is expensive and hard toimprove, resulting in difficulties in mass production. The cost oflithography using EUV lithography machines is very high.

Therefore, there is a need to provide a semiconductor device andfabrication method to provide high precision as EUV lithography providesand to satisfy the increasing demands of integrated circuit fabricationtechnology.

SUMMARY

One aspect of the present disclosure provides a method for forming asemiconductor device. The method includes forming an etch layer on asubstrate, forming a first barrier layer on the etch layer, forming afirst transitional layer on the first barrier layer, forming a pluralityof first islands on the first transitional layer by patterning the firstbarrier layer, forming a plurality of first trenches in the firsttransitional layer to expose the etch layer, the plurality of firsttrenches extending in a first direction, wherein at least a portion of afirst trench is located at each side of a corresponding first islandalong the first direction, transferring patterns of the plurality offirst trenches into the etch layer and removing the first islands,leaving a disconnected portion in a corresponding first trench at alocation of a removed first island, forming a second transitional layerand a second barrier layer on the etch layer and the plurality of firsttrenches, forming a plurality of second islands on the secondtransitional layer by patterning the second barrier layer, forming aplurality of second trenches in the second transitional layer to exposethe etch layer, the plurality of second trenches extending in the firstdirection, wherein at least a portion of a second trench is located ateach side of a corresponding second island along the first direction,and transferring patterns of the plurality of second trenches into theetch layer, wherein a second trench is disconnected at a locationcorresponding to a second island.

Another aspect of the present disclosure provides a semiconductor deviceformed by the disclosed method.

Other aspects or embodiments of the present disclosure can be understoodby those skilled in the art in light of the description, the claims, andthe drawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present disclosure.

FIGS. 1-29 illustrate structures corresponding to certain stages duringan exemplary fabrication process of a semiconductor device consistentwith various disclosed embodiments of the present disclosure; and

FIG. 30 illustrates an exemplary fabrication process of a semiconductordevice consistent with various disclosed embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of thedisclosure, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

In the semiconducting process, extreme ultraviolet (EUV) lithography isrequired to meet some high-precision requirements. However, theequipment of EUV lithography is not mature enough to be put into use,and the cost of EUV lithography is very high.

The present disclosure provides a method for forming a semiconductordevice by using a substrate, forming an etch layer on the substrate,forming a first transitional layer on the etch layer, forming aplurality of first islands on the first transitional layer, formingfirst trenches in the first transitional layer by etching; removing thefirst transitional layer and the first islands after transferring thepattern of the first trenches to the etch layer; forming a secondtransitional layer on the surface of etch layer after etching; forming aplurality of second islands on the second transitional layer; using thelocation of the second islands to form second trenches in the secondtransitional layer; and transferring the pattern on the secondtransitional layer to the etch layer, thus transferring the patterns ofthe first trenches and the second trenches together to the etch layer.

To better clarify the aforementioned objects, features, and advantagesof the present disclosure, some embodiments combined with figures aregiven below to elaborate on the present disclosure.

FIG. 30 illustrates a flowchart of an exemplary method for fabricating asemiconductor device consistent with various disclosed embodiments inthe present disclosure. FIGS. 1-29 illustrate schematic views of forminga semiconductor device at certain stages of an exemplary fabricationprocess.

FIG. 1 to FIG. 8 illustrate an exemplary method for forming firstislands according to various embodiments of the present disclosure.

Referring to FIG. 30, at the beginning of the fabrication process, asubstrate is provided and an etch layer is formed on the substrate(S01). FIG. 1 shows a schematic cross-section view of a correspondingsemiconductor structure.

Referring to FIG. 1, a substrate (not shown) is provided and an etchlayer 100 is formed on the substrate. In one embodiment, the substratehas a device structure, and the device structure includes a gate, asource, a drain, and an isolation structure; a contact plug is to beformed on the device structure.

The etch layer 100 includes at least three layers, including adielectric layer 101 on the substrate, a protective layer 102 on the topof the dielectric layer 101, and an etch-surface layer 103 on the top ofthe protective layer 102.

The dielectric layer 101 is an oxide. In one embodiment, the dielectriclayer 101 is silicon oxide.

The protective layer 102 is interposed between the dielectric layer andthe etch-surface layer 103. On the one hand, the protective layer 102facilitates close contact between the dielectric layer 101 and theetch-surface layer 103; on the other hand, the protective layer 102serves to protect the dielectric layer 101 and the substrate at thebottom of the dielectric layer 101 from being mistakenly etched beforeforming a through plug hole.

The protective layer 102 can be a single layer or a plurality of layers.When the protective layer 102 is single-layer, the etch layer 100 has athree-layer structure; when the protective layer 102 is multiple-layer,the etch layer 100 has a structure of more than three layers.

In one embodiment, the protective layer 102 is silicon nitride; in otherembodiments, the protective layer 102 may be boron nitride or titaniumnitride, or a single layer or a combination of any number of layers ofsilicon nitride, boron nitride, and titanium nitride.

In one embodiment, the etch-surface layer 103 is made of titaniumnitride, and the etch-surface layer 103 is an initial open layer, thatis, the pattern formed in early stage is first transferred onto theetch-surface layer 103. Further, the etch-surface layer 103 and theprotective layer 102 have a high selectivity. Therefore, when theetch-surface layer 103 is etched, the protective layer 102 will not beetched, so that the dielectric layer 101 at the bottom of the protectivelayer 102 is protected.

Returning to FIG. 30, a first transitional layer and a first barrierlayer are formed on the etch layer (S02). FIG. 2 shows a schematiccross-section view of a corresponding semiconductor structure.

Referring to FIG. 2, a first transitional layer 200 and a first barrierlayer 300 are formed on the etch layer 100. Specifically, the firsttransitional layer 200 is formed on the etch-surface layer 103, and thefirst barrier layer 300 is formed on the first transitional layer 200.

In one embodiment, the first transitional layer 200 is formed usingchemical vapor deposition, and the material of the first transitionallayer 200 has a high selectivity toward the material of the etch-surfacelayer 103. When the first transitional layer 200 is etched, theetch-surface layer 103 at the bottom of the first transitional layer 200will not be etched. The material of the first transitional layer 200 isan oxide. In one embodiment, the material of the first transitionallayer 200 is silicon oxide.

The first barrier layer 300 is on the top of the first transitionallayer 200, and the material of the first barrier layer 300 has a highselectivity toward the material of the first transitional layer 200.

In one embodiment, the material of the first barrier layer 300 isamorphous silicon.

Returning to FIG. 30, a plurality of first islands are formed on thefirst transitional layer (S03). FIG. 3-8 are schematic illustrationsshowing steps of forming first islands in the embodiment of the presentdisclosure.

Referring to FIG. 3, a first sacrificial layer 400 is formed on the topof the first barrier layer 300. The purpose of forming the firstsacrificial layer 400 is to pattern the first barrier layer 300, and thefirst barrier layer 300 is used to form a plurality of first islands onthe first transitional layer 200.

In one embodiment, the material of the first sacrificial layer 400 isdifferent from the material of the first barrier layer 300, so that theprocess of removing the first sacrificial layer 400 by subsequentetching does not etch and damage the first barrier layer 300. Thematerial of the first sacrificial layer 400 can be silicon oxide. Thematerial of the first sacrificial layer 400 shall have a high etchingselectivity toward the material of the first hard mask 402 and thematerial of the first barrier layer 300.

In other embodiments, the material of the first sacrificial layer 400may be silicon nitride, silicon carbide, silicon oxycarbonitride, orsilicon oxynitride.

Referring to FIG. 4, a plurality of first grooves 401 are formed in thefirst sacrificial layer 400.

The detailed step includes forming a first patterned photoresist layer(not shown in the figure) on the first sacrificial layer 400 and etchingthe first sacrificial layer 400 by using the first patterned photoresistlayer as a mask to form a plurality of first grooves 401.

In one embodiment, the method of etching the first sacrificial layer 400is dry etching, and the gas includes an etching gas and a carrier gas.The etching gas includes one or more of CF₄, CHF₃, CH₂F₂, and CH₃F. Thecarrier gas is hydrogen, nitrogen, or an inert gas. Specifically, theetching gas can be CF₄, the flow rate is 50 standard mL/min to 150standard mL/min, the etching chamber temperature is 10 degrees Celsiusto 60 degrees Celsius, the etching chamber pressure is 10 mTorr to 50mTorr, and the etching time is 15 seconds to 50 seconds.

In one embodiment, the pattern of the first patterned photoresist isrectangular and distributed at desired positions.

Referring to FIG. 5, the first grooves 401 are filled with a first hardmask material 402.

In one embodiment, the process of filling the first grooves 401 with thefirst hard mask material 402 is a chemical vapor deposition process or aphysical vapor deposition process. After filling the first hard maskmaterial 402, the first hard mask material 402 is planarized until thetop surface of the first sacrificial layer 400 is exposed, only keepingthe first hard mask material 402 in the first grooves 401.

In one embodiment, the planarization process is a chemical mechanicalpolishing process.

In one embodiment, the first hard mask material 402 can be siliconnitride, ensuring a high etching selectivity between the first hard maskmaterial 402 and the first barrier layer 300 and the first sacrificiallayer 400.

After filling the first hard grooves 401 with the first hard maskmaterial 402, the method further includes removing the first sacrificiallayer 400 and retaining the first hard mask material 402 inside thefirst grooves 401 (not shown in the figure).

In one embodiment, the process of removing the first sacrificial layer400 is a wet removal process, and the first sacrificial layer 400 isremoved by using a hydrofluoric acid solution.

In other embodiments, when the material of the first sacrificial layer400 is silicon nitride, the first sacrificial layer 400 is removed byetching using a phosphoric acid solution.

Referring to FIG. 6, the first barrier layer 300 is etched by using thefirst hard mask material 402 as a mask to form the first islands 300 a.

Referring to FIG. 7, the first hard mask material 402 is removed, andthe first island 300 a is retained on the first transitional layer 200.

Referring to FIG. 8, FIG. 8 is a top view of FIG. 7, and FIG. 7 is across-sectional view of FIG. 8 in the direction of line AA1. It can beseen that the plurality of first islands 300 a are distributed on thefirst transitional layer 200.

It should be noted that, in the process of forming the first islands 300a, an etching selectivity needs to be ensured between adjacentmaterials.

FIG. 9 to FIG. 14 are partial schematic illustrations showing steps offorming first trenches in the embodiment of the present disclosure.

Returning to FIG. 30, a plurality of first trenches are formed in thefirst transitional layer to expose the etch layer (S04). FIG. 9 is aschematic illustration showing the formation of the first trenches onthe first transitional layer; and FIG. 10 is a cross-sectional view ofFIG. 9 in the direction of line B-B1.

In one embodiment, a second patterned photoresist layer (not shown) isformed on the first transitional layer 200. The second patternedphotoresist layer and the first islands 300 a are used as masks foretching the first transitional layer 200 to form a plurality of firsttrenches 500 in the first transitional layer 200. The bottom of thefirst trenches 500 exposes a portion of the surface of the etch-surfacelayer 103.

Referring to FIG. 9, a plurality of first trenches 500 extend in a firstdirection x. Since the first islands 300 a are used as masks duringetching, at least part of the first trenches 500 are located on bothsides of the corresponding position of the first islands 300 a. In a topview, the first trenches 500 are disconnected by the first islands 300 ain the first direction x. Moreover, the opening width of the firsttrenches 500 perpendicular to the first direction x is smaller than thewidth of the first islands 300 a.

Returning to FIG. 30, patterns of the first trenches are transferredinto the etch layer and the first islands are removed (S05). FIG. 11 isa schematic illustration showing partial steps of transferring thepattern of the first trenches 500 into the etch layer 100; and FIG. 12is a cross-sectional view of FIG. 11 along the direction of line B3-B4.

Referring to FIG. 11 and FIG. 12, the etch-surface layer 103 is etchedbased on the shape of the first trenches 500 to open the etch layer, andthe first trenches 500 are formed in the etch-surface layer 103. Thedielectric layer 102 is exposed at the bottom of the first trenches 500.The first island 300 a is removed after the etching layer is opened.

In one embodiment, the material of the etch-surface layer 103 istitanium nitride, and the method of etching the etch-surface layer 103is a dry etching process. The gas includes an etching gas and a carriergas. The etching gas includes one or more of chlorine, nitrogen, ormethane, and the carrier gas is hydrogen, nitrogen, or an inert gas.Specifically, the etching gas can be nitrogen gas, the gas flow rate is0 standard mL/min to 100 standard mL/min, the etching chambertemperature is 10 degrees Celsius to 60 degrees Celsius, the etchingchamber pressure is 10 mTorr to 150 mTorr, and the etch time is 5seconds to 20 seconds.

In one embodiment, the process of removing the first islands 300 aincludes a wet removal, such as a wet etching.

In other embodiments, the first islands 300 a can be removed first, thenetching along the first trenches 500 to open the etch layer 100.

FIG. 13 is a schematic illustration showing the structure after theremoval of the first transitional layer 200. FIG. 14 is across-sectional view of FIG. 13 along the direction of line B5-B6.

Referring to FIG. 13 and FIG. 14, the first transitional layer 200 isremoved.

In one embodiment, the process of removing the first transitional layer200 is wet etching. Since the material of the first transitional layer200 is silicon oxide, it is removed by using a hydrofluoric acidsolution.

It should be noted that the pattern of the first trenches 500 istransferred to the etch layer 100, and only the etch-surface layer 103of the etch layer is opened, so that the etch layer 100 can be used formultiple times to form more complex patterns.

FIG. 15 to FIG. 27 are schematic illustrations showing the steps offorming second trenches in the embodiment of the present disclosure.

Returning to FIG. 30, a second transitional layer and a second barrierlayer are formed on the etch layer and the first trenches (S06). FIG. 15to FIG. 18 show the steps of forming the second transitional layer andthe second barrier layer.

Referring to FIG. 15, a second transitional layer 210 is formed on thesurface of the etch-surface layer 103, the bottom of the first trenches500, and the sidewall of the first trenches 500.

In one embodiment, the process of forming the second transitional layer210 is a chemical vapor deposition method. The material of the secondtransitional layer 210 has a high selectivity toward the material of theetch-surface layer 103. When the second transitional layer 210 isetched, the etch-surface layer 103 at the bottom of the secondtransitional layer 210 will not be etched. The material of the secondtransitional layer 210 is an oxide. In one embodiment, the material ofthe second transitional layer 210 is silicon oxide.

Referring to FIG. 16, a second barrier layer 310 is formed on the uppersurface of the second transitional layer 210, and the material of thesecond barrier layer 310 has a high selectivity toward the material ofthe second transitional layer 210. The second barrier layers 310 areused to form second islands, as in the foregoing method of forming thefirst islands 300 a.

Referring to FIG. 17 and FIG. 18, FIG. 18 is a top view of FIG. 17,while FIG. 17 is a cross-sectional view of FIG. 18 along the directionof line CC1, wherein the dotted lines are the position of the firsttrenches 500 formed in previous steps. A second sacrificial layer 410 isformed on the second barrier layer 310, and the second sacrificial layer410 is overlaid on the second barrier layer 310.

In one embodiment, the material of the second sacrificial layer 410 isdifferent from the material of the second barrier layer 310, so that theprocess of removing the second sacrificial layer 410 by subsequentetching does not etch and damage the second barrier layer 310. Thematerial of the second sacrificial layer 410 can be silicon oxide. Thematerial of the second sacrificial layer 410 shall have a high etchingselectivity toward the material of the second barrier layer 310.

In other embodiments, the material of the second sacrificial layer 410can also be silicon nitride, silicon carbide, silicon oxycarbonitride,or silicon oxynitride.

Returning to FIG. 30, a plurality of second islands are formed on thesecond transitional layer (S07). FIG. 19 to FIG. 23 are schematicillustrations showing a process of forming second islands 310 a.

First, a third patterned photoresist layer (not shown) is formed on thesecond sacrificial layer 410. In one embodiment, the pattern of thethird patterned photoresist layer is rectangular and distributed atdesired positions. The pattern of the third patterned photoresist layeris transferred to the second barrier layer 310 by using the thirdpatterned photoresist layer as a mask to etch the second sacrificiallayer 410, forming a plurality of second grooves. The second grooves arelocated between adjacent first trenches 500.

In one embodiment, the method of etching the second sacrificial layer410 is dry etching, and the gas includes an etching gas and a carriergas. The etching gas includes one or more of CF₄, CHF₃, CH₂F₂, and CH₃F.The carrier gas is hydrogen, nitrogen, or an inert gas. Specifically,the etching gas can be CF₄, the flow rate is 50 standard mL/min to 150standard mL/min, the etching chamber temperature is 10 degrees Celsiusto 60 degrees Celsius, the etching chamber pressure is 10 mTorr to 50mTorr, and the etching time is 15 seconds to 50 seconds. Referring toFIG. 19, a second hard mask material 412 is formed in the secondgrooves.

In one embodiment, the process of forming the second hard mask material412 in the second grooves is a chemical vapor deposition process or aphysical vapor deposition process. After filling the second hard maskmaterial 412, the second hard mask material 412 is planarized until thetop surface of the second sacrificial layer 410 is exposed, only keepingthe second hard mask material 412 in the second grooves.

In one embodiment, the planarization process is a chemical mechanicalpolishing process.

In one embodiment, the second hard mask material 412 can be siliconnitride, ensuring a high etching selectivity between the second hardmask material 412, the second barrier layer 310, and the secondsacrificial layer 410.

Referring to FIG. 21, the second barrier layer 310 is etched by usingthe second hard mask material 412 as a mask to form the second islands310 a.

Before the second barrier layer 310 is etched to form the second islands310 a, the method further involves removing the second sacrificial layer410 and retaining the second hard mask material 412 in the secondgrooves.

In one embodiment, the process of removing the second sacrificial layer410 is a wet removal process, and the second sacrificial layer 410 isremoved by using a hydrofluoric acid solution.

In other embodiments, when the material of the second sacrificial layer410 is silicon nitride, the second sacrificial layer 410 is removed byusing a phosphoric acid solution.

Referring to FIG. 22 and FIG. 23 (FIG. 22 is a cross-sectional view ofFIG. 23 in the direction of the tangential line C4C5), the second hardmask material 412 is removed, while the second islands 310 a areretained, and the second islands 310 a are located on the top of thesecond transitional layer 210.

It should be noted that, in the process of forming the second islands310 a, an etching selectivity needs to be ensured between adjacentmaterials.

Returning to FIG. 30, a plurality of second trenches are formed in thesecond transitional layer to expose the etch layer (S08). FIG. 24 toFIG. 27 are schematic illustrations showing steps of forming secondtrenches in the embodiment of the present disclosure.

Among them, FIG. 24 is a schematic view showing the formation of thesecond trenches in the second transitional layer 210; and FIG. 25 is across-sectional view of FIG. 24 in the direction of line C6-C7.

Referring to FIG. 24, second trenches 510 are formed in the secondtransitional layer 210.

The specific steps involve forming a fourth patterned photoresist layer(not shown) on the second transitional layer 210, using superposedpatterns of the fourth patterned photoresist layer and the second island300 a as masks for etching the second transitional layer 210 to form aplurality of second trenches 510 in the second transitional layer 210,and exposing a portion of the surface of the etch-surface layer 103through the bottom of the first trenches 510.

The plurality of second trenches 510 extend in a first direction x.Since the second islands 310 a are used as masks during etching, atleast part of the second trenches 510 are located on both sides of thecorresponding position of the second islands 310 a. In a top view, thesecond trenches 510 are disconnected by the second islands 310 a in thefirst direction x. Moreover, the opening width of the second trenches510 perpendicular to the first direction x is smaller than the width ofthe second islands 310 a.

Referring to FIG. 25, when the plurality of second trenches 510 areformed, the second transitional layer 210 covering the inner side walland the bottom of the first trenches 500 is removed, so that the firsttrenches 500 are opened to expose the protective layer 102.

Referring to FIG. 26, etching continues along the shape of the secondtrenches 510 in the second transitional layer 210, opening theetch-surface layer 103, transferring the pattern of the second trenches510 to the etch-surface layer 103, and removing the second islands 310a.

The material of the etch-surface layer 103 is titanium nitride. Themethod of etching the etch-surface layer 103 is a dry etching process,and the process of removing the second island 310 a is wet removal.

In other embodiments, the second islands 310 a can be removed firstbefore etching along the second trenches 510 to open the etch layer 100.

Referring to FIG. 27, the second transitional layer 210 is removed.

The shape of the pattern in the etch-surface layer 103 is retained, andthe shape of the pattern is the combined shape of the first trenches 500and the second trenches 510.

In one embodiment, the process of removing the second transitional layer210 is wet etching. Since the material of the second transitional layer210 is silicon oxide, it is removed by using a hydrofluoric acidsolution.

Returning to FIG. 30, patterns of the second trenches are transferredinto the etch layer (S09). FIG. 28 is a top view illustrating thestructure by etching through the protective layer 102 and the dielectriclayer 101; and FIG. 29 is a cross-sectional view along line D-D1 of thestructure illustrated in FIG. 28.

Referring to FIG. 28 and FIG. 29, etching is continued in the protectivelayer 102 and the dielectric layer 101 following the shape of the firsttrenches 500 and the second trenches 510 in the etch-surface layer 103to completely etch through the etch layer 100.

In one embodiment, a dry etching is used to etch through the protectivelayer 102 and the dielectric layer 101, although any suitable etchingmethods may also be used in accordance with various embodiments. The gasincludes an etching gas and a carrier gas. The etching gas includes oneor more of CF₄, CHF₃, CH₂F₂, and CH₃F. The carrier gas is hydrogen,nitrogen, or an inert gas.

The present disclosure also provides a semiconductor structure formed bythe disclosed method. The present disclosure provides a method foretching and forming a shape of a target pattern satisfying thehigh-precision requirements on the etch-surface layer 103, and using thecurrently mature nanolithography technology to completely etch throughthe etch layer 100 following the target pattern and achieving the highprecision of semiconductor fabrication.

As disclosed, the technical solutions of the present disclosure have thefollowing advantages: forming an etch layer on a substrate; forming afirst transitional layer on the etch layer; forming a plurality of firstislands on the first transitional layer; using the locations of thefirst islands on the first transitional layer to etch and form firsttrenches; after transferring the pattern of the first trenches to theetch layer, removing the first transitional layer and the first islands;etching the surface of the etch layer to form a second transitionallayer; forming second islands on the second transitional layer; etchingsecond trenches on the second transitional layer by using the locationsof the second islands; transferring the pattern on the secondtransitional layer to the etch layer, such that the patterns of both thefirst trenches and the second trenches are transferred together onto theetch layer. After transferring the patterns of both the first trenchesand the second trenches together onto the etch layer, the etch layer iscompletely opened there-through. As such, high-precision fabrication ofsemiconductor devices is achieved and use of EUV lithography is avoided.

The embodiments disclosed herein are exemplary only. Other applications,advantages, alternations, modifications, or equivalents to the disclosedembodiments are obvious to those skilled in the art and are intended tobe encompassed within the scope of the present disclosure.

What is claimed is:
 1. A method for forming a semiconductor device,comprising: forming an etch layer on a substrate; forming a firsttransitional layer on the etch layer; forming a first barrier layer onthe first transitional layer; forming a plurality of first islands onthe first transitional layer by patterning the first barrier layer;forming a plurality of first trenches in the first transitional layer toexpose the etch layer, the plurality of first trenches extending in afirst direction, wherein at least a portion of a first trench is locatedat each side of a corresponding first island along the first direction;transferring patterns of the plurality of first trenches into the etchlayer and removing the first islands, leaving a disconnected portion ina corresponding first trench at a location of a removed first island;forming a second transitional layer and a second barrier layer on theetch layer and the plurality of first trenches; forming a plurality ofsecond islands on the second transitional layer by patterning the secondbarrier layer; forming a plurality of second trenches in the secondtransitional layer to expose the etch layer, the plurality of secondtrenches extending in the first direction, wherein at least a portion ofa second trench is located at each side of a corresponding second islandalong the first direction; and transferring patterns of the plurality ofsecond trenches into the etch layer, wherein a second trench isdisconnected at a location corresponding to a second island.
 2. Themethod according to claim 1, wherein forming the plurality of firstislands on the first transitional layer by patterning the first barrierlayer includes: forming a first sacrificial layer on the first barrierlayer; forming a first patterned photoresist layer on the firstsacrificial layer; and transferring a pattern of the first patternedphotoresist layer to the first barrier layer.
 3. The method according toclaim 2, wherein transferring the pattern of the first patternedphotoresist layer to the first barrier layer includes: etching the firstsacrificial layer to form a plurality of first grooves by using thefirst patterned photoresist layer as a mask; filling the first grooveswith a first hard mask material; removing the first sacrificial layerand retaining the first hard mask material in the first grooves; etchingthe first barrier layer by using the first hard mask material as a maskto form the plurality of first islands; and removing the first hard maskmaterial on the plurality of first islands.
 4. The method according toclaim 3, wherein removing the first sacrificial layer includes a wetremoval process.
 5. The method according to claim 3, wherein etching thefirst hard mask material includes dry etching.
 6. The method accordingto claim 3, wherein the first hard mask material includes siliconnitride.
 7. The method according to claim 1, wherein forming theplurality of first trenches in the first transitional layer includes:forming a second patterned photoresist layer on the first transitionallayer; etching the first transitional layer using the second patternedphotoresist layer and the plurality of first islands as a mask; andforming the plurality of first trenches.
 8. The method according toclaim 1, wherein after transferring the pattern of the first trenchesinto the etch layer, the method further includes removing the pluralityof first islands and the first transitional layer.
 9. The methodaccording to claim 8, wherein removing the plurality of first islandsand the first transitional layer includes wet etching.
 10. The methodaccording to claim 1, wherein forming the plurality of second islands onthe second transitional layer by patterning the second barrier layerincludes: forming a second sacrificial layer on the second barrierlayer, filling the plurality of first trenches with the secondsacrificial layer; and forming a third patterned photoresist layer onthe second sacrificial layer and transferring a pattern of the thirdpatterned photoresist layer to the second barrier layer.
 11. The methodaccording to claim 10, wherein transferring the pattern of the thirdpatterned photoresist layer to the second barrier layer includes: usingthe third patterned photoresist layer as a mask to etch the secondsacrificial layer and to form second grooves, and the second grooves arelocated between adjacent first trenches; filling the second grooves witha second hard mask material; removing the second sacrificial layer andretaining the second hard mask material in the second grooves; etchingthe second barrier layer by using the second hard mask material as amask to form the plurality of second islands; and removing the secondhard mask material on the plurality of second islands.
 12. The methodaccording to claim 11, wherein the second hard mask material is siliconnitride.
 13. The method according to claim 11, wherein removing thesecond sacrificial layer is a wet removal process.
 14. The methodaccording to claim 1, wherein forming the plurality of second trenchesin the second transitional layer includes: forming a fourth patternedphotoresist layer on the second transitional layer; etching the secondtransitional layer by using the fourth patterned photoresist layer andthe second islands as a mask; and forming the plurality of secondtrenches.
 15. The method according to claim 14, wherein after formingthe plurality of second trenches, the method further includes:transferring the pattern of the plurality of first trenches into theetch layer and removing the pattern of second islands; and removing thesecond transitional layer.
 16. The method according to claim 15, whereinremoving the pattern of second islands and the second transitional layerincludes a wet etching.
 17. The method according to claim 1, wherein theetch layer has a structure with at least three layers.
 18. The methodaccording to claim 17, wherein when the etch layer is a three-layerstructure, the etch layer includes a dielectric layer, a protectivelayer on the dielectric layer, and an etch-surface layer on theprotective layer.
 19. The method according to claim 1, wherein a patternof the plurality of first trenches and the plurality of second trenchesis transferred to the etch-surface layer, and a pattern of theetch-surface layer is transferred to the dielectric layer.